1. Field of the Invention
The present invention relates to an illumination device, and more particularly to a polarized light illumination device.
2. Related Art
Along with the enhanced light-emitting efficiency and high color performance of the light-emitting diode (LED), many projection systems taking the liquid crystal display (LCD), liquid crystal on silicon (LCoS) or digital mirror device (DMD) as an imaging device have adopted the LED as a light source for the imaging projection device, in order to achieve a better color performance and the objective of being light, thin, short, and small. Besides being applied in the above projection displays, the LED light source also becomes a main light source for the LCD under the consideration of the highly-developed LCD technique and the environmental problem caused by the cold cathode fluorescent lamp (CCFL). However, since the LCD can receive merely the light source at a unidirectional polarization state, the LCD display adopting the LED as the light source may lose ½ light energy, if the conversion and utilization of the polarization state are not taken into consideration, as a result, the quality and efficiency of the display may be greatly reduced.
U.S. Pat. No. 7,070,300 has disclosed an illumination system. In order to enhance the brightness of the illumination system, a phosphor layer is employed for wavelength conversion, so that the converted light is prevented from damaging the light source once it is incident back on the light source. However, the illumination device further requires another receiver for converting the wavelength, and thus the volume of the illumination device is increased. Moreover, since the display device is mostly in the shape of rectangle, the light of the illumination system cannot be easily modified into a rectangular shape, so as to cause unnecessary loss of light energy.
U.S. Pat. No. 6,318,863 has disclosed an illumination device and image projection apparatus including the same. The illumination device includes: a light source, as an array formed by a plurality of light-emitting modules; and an array of taper light pipes, formed by a plurality of taper light pipes, wherein each taper light pipe has a first end and a second end. The first end of the taper light pipe is tightly connected to the light-emitting module, and thus the wide angle light emitted by each light-emitting module is collected and then converted into narrow angle light. Therefore, uniform light is emitted from the second end of each taper light pipe and projected on the light valve for imaging. Under the condition of the conservation of etendue, a taper light pipe is used in this patent to reduce the light exit angle distribution, so as to uniform the lights. The light exit angle of the LED light source is an approximate lambertian distribution. In other words, the area of the light exit port of the taper light pipe must be sufficient large to reach a specific range, so as to effectively reduce the light exit angle of the light source. Therefore, since the area of the panel is limited, the number of the LEDs disposed thereon is somewhat restricted, so as to greatly reduce the efficiency of the illumination system.
U.S. Pat. No. 6,414,438 has disclosed a polarized light illumination and a projection display. The projection display converts the polarization state of light through a polarized converting element, so as to enhance the efficiency of the system. However, due to the system configuration, the incident light must be controlled at an angle within a certain range, and the polarized converting element can be used merely under a specific system configuration, and as a result, it is not suitable for other systems.
ROC Patent No. 1269112 has disclosed an optical projection device and a polarized light source module thereof. The polarized light source module includes a light source, a reflector, and an optical film with a polarized light splitter and a polarized light converting reflector. The light source provides a non-polarized light, the reflector has a curved surface, and the reflector and the optical film wrap the light source. The polarized light splitter allows the first polarized light to pass through, and reflects the second polarized light towards the polarized light converting reflector through the curved surface. The polarized light converting reflector is used to convert the second polarized light into the first polarized light for being reflected, and the first polarized light reflected by the polarized light converting reflector is reflected by the reflector and then passes through the polarized light splitter. The etendue of the polarized light source module is rather low, thus the optical projection device may has a lower manufacturing cost and a higher light utilization rate, but the volume of the polarized light source module still needs to be improved.
In view of the above, the polarized conversion module currently used in the LCD or projection system mostly adopts a spacially separated configuration, i.e., the two portions of light at different polarization directions are spacially separated and then processed separately, so as to improve the efficiency of the device. Due to the etendue, if the light from the light source is converted after being emitted to the system for a certain distance, it easily results in an enlarged system volume.
Therefore, how to provide a polarized light illumination device with a high efficiency and the characteristics of being light, thin, short, and small has become one of the problems to be solved by the researchers.